After reportedly suffering four concussions in the past five years, Arizona State quarterback Steven Threet has decided he'll no longer play football.

Threet played in 11 games last season, completing 61.9 percent of his pass attempts for 2,534 yards and 18 touchdowns with 16 interceptions. In two of those appearances, at Cal on Oct. 23 and against UCLA on Nov. 26, Threet was knocked out of action due to concussion.

Following the second of his concussions last season, Threet was replaced early in the Sun Devils' final home game of the season by sophomore Brock Osweiler, who went on to complete 27 of 36 passes for 380 yards and four touchdowns in the 55-34 win over the Bruins.

With Threet ruled out by team doctors, Osweiler started against Arizona in the final game of the season, leading the team to a thrilling 30-29 double overtime win.

As a result of how the season ended, it appeared Osweiler was the leading candidate to become the team's starter in 2011, though coach Dennis Erickson said prior to Wednesday's announcement the quarterback competition remained open entering the spring.

As it stands now, Osweiler is the prohibitive favorite to win the job this season. Redshirt freshman Taylor Kelly and true freshman Michael Bercovici, a spring enrollee, are the only other scholarship quarterbacks on the roster this semester after senior-to-be Samson Szakacsy left the program last month.